Cristiano Ronaldo has left the door open to a potential future move to Serie A by claiming he would \"never say never\" to playing in Italy. The Portuguese attacker joined Real Madrid in 2009 from Manchester United and has since gone on to score 143 goals for the club in 141 appearances.Despite claiming he is happy in Spain, the 27-year-old did concede that he would not rule out a switch to the Italian top flight and revealed his admiration for the \'big three\' in Serie A. \"I respect the Italian league but right now it is third behind Spain\'s [La Liga] and England\'s [Premier League]. But never say never. Someday, why not In Italy? There are fantastic teams like Inter, AC Milan and Juventus,\" the forward told Mediaset. \"I\'m proud to play for Real Madrid because I have fun; when you no longer have fun it\'s a sign that it\'s time to leave. For now though, I\'m happy here at the greatest club in the world.\" Ronaldo also spoke positively of his coach and compatriot, Jose Mourinho, stating that the 49-year-old is the No.1 trainer in the world. \"Mourinho is an amazing coach and his trophies say it all: he\'s won in Portugal, England and Italy, and this makes him the best,\" he added. \"To me, being the best means proving it in different countries and championships, Unlike others, Mourinho has done exactly that; it\'s simple.\" The Madeira-born star is expected to be in action for Los Blancos on Wednesday evening when the Spanish giants can be crowned Liga champions with victory away at Athletic Bilbao. Starting last month and continuing for 10 weeks, Goal.com is publishing exclusive extracts from Luca Caioli\'s new book, Ronaldo: The Obsession for Perfection. The sixth extract, published on Friday, looks at his display for Man Utd in the 2008 Champions League final against Chelsea in Moscow, including the Portuguese\'s missed penalty in the shoot-out. Don\'t miss it!